1. Field of the Invention
The present invention relates to a lamp having light emitting diodes as light source, and suited for use as an automobile lamp, a room lamp of hotel or house, a night signal, especially a tail lamp of an automobile.
2. Prior Art of the Invention
There has been used a tail lamp of automobile which has a filament as a light source. However, the tail lamp of filament type has many shortcomings, such as consuming too much electric power, generating a great amount of heat, employing a readily snapping filament, and the lamp per se being large and heavy or the like.
In order to overcome these problems, it has been proposed that instead of the filament lamp, a light emitting diode lamp is adopted, which has such a structure that a plurality of light emitting diodes are mounted on an insulating board. The proposal may overcome the above problems on the conventional filament lamp, because light emitting diodes emit light by a lower voltage and current than those of filament lamp, and also is small and light, and seldom include problem of snapping, thus realizing low electric power consumption, low heat generation, substantially no snapping to be able to use semipermanently, small size, and light weight.
However in this proposal there has been the following new problem; that is, tail lamps of automobiles have in general a wider window through which light from its light source is released forward, and it is required that the light released from the window is neither too strong nor too weak, or should be moderate, and also is released as even as possible all over the window. When the window is filled up with light emitting diodes in order to achieve even lighting, the lighting power becomes too strong to fail as a tail lamp of automobile. On the other hand, when using a small number of light emitting diodes in order to make power moderate, the lighting becomes spot-like, and therefore it does not obtain a lamp which illuminates evenly.